AU677169B2

AU677169B2 - Tubeless tyre beads and methods for manufacturing same

Info

Publication number: AU677169B2
Application number: AU32575/93A
Authority: AU
Inventors: Jean Billieres
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 1991-12-31
Filing date: 1992-12-21
Publication date: 1997-04-17
Anticipated expiration: 2012-12-21
Also published as: EP0619784B1; MX9207576A; AU3257593A; ES2092280T3; EP0619784A1; CA2122013C; DE69213762D1; CA2122013A1; NZ246340A; DE69213762T2; FR2685666A1; US5499670A; WO1993012943A1; JPH07502471A; BR9206934A

Description

OPI DATE 28/07/93 AOJP DATE 30/09/93 APPLN. ID 32575/93 PCT NUMBER PCT/EP92/02972 AU9332575 DEMANDE INTERNATIONALE PUBLIEE EN VERTU DU TRAITE DE COOPERATION EN MATIERE DE BREVETS (PCT) (51) Classification internationale des brevets 5 (11) Num(~ro de publication internationale: WVO 93/12943 5/16 Al (43) Date de publication internationale: 8Sjuillet 1993 (08.07.93) (21) Numi~ro de la demnande internationale: PCT/EP92/02972 1(74) Mandataire: DEVAIJX, Edmond-Yves; Michelin Cie, Service SRK. Brevets, F-63040 Clermont-Ferrand C~dex (22) Date de d~p6t international: 21 d~cembre 1992 (21.12.92) (FR).

Donnkes relatives i la priorit6: (81) Etats disign~s: A U, BR, CA, JP, NZ, US, brevet europ~en 91/16458 316dcembre 1991 (31.12.91) FR (AT, BE, CH, DE, DK, ES, FR, GB, GR, IF., IT, LU, MC, NL, PT, SE).

(71) D~posant (pour tous les Etats d~signks satif US): COM PA- GNIE GENERALE DES ETABLISSEMENTS MI- Publiie CHELIN MICHELIN CIE [FR/FR]; 12, cours Sa- Avec rapport de recherche internationale.

blon, F-63040 Clermont-Ferrand C~dex (FR).

(72) Inventeur; et 1nventeur/Diposant (US seulement) BILLIERES, Jeanq [FR/FR]; 7, rue du Parc de Montjuzet, F-63100 Cler- I I mont-Ferrand (FR).

(54) Title: TUBELESS TYRE BEADS AND METHODS FOR MANUFACTURING SAME (54)Titre: BOURRELETS DE PNEUMATIQUES SANS CHAMBRE A AIR ET LEURS PROCEDES DE FABRICATION (57) Abstract Tubeless tyre bead structures having enhanced rim-sealing and wear resistance properties. At least the rim-engaging surfaces of the beads consist of protective mixtures and the rim-engaging portion of the protective material is at least partially coated with a waterproof mixture An extension of the coating over the surface of the protective material which contacts the air in the tyre is desirable.

(57) A~r~g6 L'invention concerne les structures et leurs r~alisations de bourrelets de pneumatiques sans chambre A air, dont les caract~ristiques d'ktanch~it6 sur les jantes et la resistance aux degradations sont augment~es. Les bourrelets dont au momns les surfaces de contact sur les jantes sont constitu~es de m~langes protecteurs sont recouverts selon 1'invention de melange impermeable au momns partiellement sur la partie du protecteur au contact avec la jante. Le prolongement du recouvrement sur la surface du protecteur au contact de F'air de gonflage est souhtaitable.

I

Beads of Tubeless Tires and Methods for Producing Them The invention relates to tires of the so-called "tubeless" type and, more particularly, to the beads of such tires.

Such tires, which are widely used, particularly for trucks, have a radial carcass reinforcement which is reinforced with cables located approximately in planes including the axis of rotation of the tire, surmounted by a crown reinforcement and a tread, the carcass ply or plies being wound at each of their two ends around a substantially unstretchable bead ring.

In the case of tubeless tires, it is necessary that the inflation atmosphere not be subjected to losses by diffusion into the materials of the mounted assembly or by leaks caused by.a poor seal of the different connecting surfaces between tire and rim.

In order to minimize the diffusion phenomena as far as possible, the inner surface of these tires is generally covered with a layer of "inner rubber" selected for its excellent impermeability properties. In general, the vulcanized rubbers used for this internal layer do not have good mechanical properties since they are frequently formulated with rubbers having a base of polyiosbutylene or their substantially non-unsaturated, slightly reinforced derivatives in order to optimize the properties of impermeability, resilience, deformability, and adhesion to the carcass. French patent application 72/43974 published under number 2162667 and claiming priority from United Kingdom patent application 47648/1971 filed 11 December, 1971 in the name of Dunlop Limited, describes this aspect of the prior art.

In ornder to minimize the leaks possible at the contact interfaces of the beads on the rim, particular care must be taken in the design and production of these surfaces, as well as in maintaining them in good condition. Tightness is assured by good pressure contact of the beads of the tires on the rims, the clamping force being assured by the internal pressure of the inflation atmosphere and the shapes of the surfaces which rest against each other.

The contact between the bead of the tire and the rim must also assure good transmission of the mechanical forces resulting from the driving or braking torques by a connection which is without substantial slippage, avoiding :i 15 excessively rapid wear of the surfaces of the bead. In order to fulfil this role, the vulcanized rubber touching the rim and forming the transition with the carcass reinforcement and the bead ring or rings has high values of hardness and modulus of elasticity. It is generally formulated with elastomers which are generally very unsaturated, highly loaded and cross-linked. This mix, which 20 also assures a role of protecting the bead ring or rings and the carcass i; reinforcement or reinforcements is frequently known as a "protector", since it in particular avoids direct injuries to them by the tools 0 S o

S

4 o o i M eo° 3 used upon the operations of mounting and dismounting the tire on-its rim.

Tire carcass reinforcements have experienced substantial improvements in quality which makes it possible to reuse them several times by retreading the portion which has become worn in contact with the ground. The surfaces and/or edges of the rubber of the beads are therefore subjected to more frequent mounting and dismounting operations, which can damage them.

Furthermore, the beads are subjected to greater aging stresses, due to the longer operating life of the carcasses.

In fact, after prolonged tests of tires mounted on rims subjected to heating due to braking, deterioration is noted in the adherence of the carcass reinforcement cables in the region of the beads, as well as a change in the properties of the protector in contact with the rims and of the part in contact with the inflation air; these parts of the protector are substantially hardened and may even thereby become much too fragile and brittle. This hardening and the cracking which results from it favor leakage of the inflation air.

The object of the present invention is to overcome said drawbacks by partially covering the protector, formed in part of vulcanized rubber of high stiffness close to the protectors of the prior art by a layer of a mix which is much more impermeable, which may be close to the formulations and properties of the sealing rubber, thus assuring the contact with the rim in an unusual manner. A substantial increase is 4 noted in the life of the protectors and of the underlying plies and reinforcements, thus solving the problems encountered, in particular with respect to the mechanical properties and seal of beads, without impairing the other properties or the performance of the tire; In accordance with the invention, a tubeless tire having carcass reinforcement which is integral with bead rings and covered on the inside by a layer of rubber of slight stiffness which is impermeable to the inflation air, the beads being covered, at least in the part thereof in contact with the rim, by circumferential profiled members known as protectors, formed of non-impermeable rubbers of high stiffness, is characterized by the fact that the protectors are partially covered, at least radially to the inside and axially towards the inside by a layer of impermeable mix, that is to say, having a coefficient of permeability to air at 80 0 C less than -17 2 21 x 10 x m and preferably less than s x Pa 14x1 17 2 14 x 10 x m and, more particularly, less than s x Pa -17 2 7 x 10 17 x m and of a thickness of between 0.1 s x Pa and 1 mm, covering the radially inner part of the protector over an axial length such that the ratio of said length to the axial width of the bead is between 0.2 and 0.7, without being penalized by the drawbacks resulting from the presence 5 of a slightly-rigid mix in contact with the rim, namely poor clamping of the tire on its rim, which would result in poor transmission of the driving and braking torques, and poor mechanical resistance of the bead, with excessive abrasion.

One can, in fact, accept for this impermeable mix rather low values of rigidity, expressed by the modulus at elongation E10 force/initial section between 1.5 and 8 MPa, even on the radially most inner part of the protector.

In accordance with another aspect of the invention, it is advantageous for the layer of impermeable mix added on the beads to assure continuity by contact with the sealing rubber covering the inner side of the tire. It is nevertheless of interest to produce tires the protectors of which are covered with impermeable mix only primarily on the portion touching the seats of the rim, or primarily on the surface in contact with the inflation air. This layer of impermeable mix used in accordance with these provisions greatly slows down the degradation of the protector and of the underlying plies, which will permit more numerous repeated use of the carcass by retreading. The solution proposed by the invention may, it is believed, combat the harmful effects of the oxygen of the inflation air which can infiltrate between the protector and the rim from the inside of the tire and pass axially towards the heel of the bead. This infiltration could be due to the decrease in the clamping forces in the axially inner zone of the bead upon the forces during travel.

Yvro A 7- O 6 The sole figure of the accompanying drawing will make it more easily understood how the invention can be reduced to practice.

This figure shows a cross section in the zone of a bead B mounted on its seat J in the case of a tire in accordance with the invention. A carcass reinforcement 1 is anchored to a bead ring 2 in the bead B, forming an upturn 10 which is folded onto rubber fillings 3 and supplemented by a stiffener 4 contained between two layers of rubber 41 and 42 and located axially to the outside of the upturn 10. The carcass reinforcement 1 is covered towards the inside by a layer of reinforcement rubber 5, itself covered by a layer of inner rubber 6 of a thickness of between 1 and 3 mm, selected for its impermeability characteristics, and terminating in the inner part or tip P of the bead.

The bead B of the prior art is covered axially to the outside, radially to the inside and axially to the inside along a portion of the outer course of the plies or rubbers (42, 4, 41, i, 5, 6) by a protector 7 formed generally of a very rigid vulcanized rubber having good properties of resistance to wear on the rim.

In accordance with the invention, this protector 7 is covered by a layer of air-impermeable mix 8 which may or may not be of the same composition as the inner rubber 6. This layer 8 extends axially below the seat of the bead B over a distance LO measured from the tip of the bead such that its 7 ratio LO/L1 to the total width LI of the seat of the bead is between 0.2 and 7. The layer 8 is furthermore of a substantially constant thickness 1 of between 0.1 and 1 mm.

It can be extended towards the inside in a radial.direction with a thickness 1' of between 0.1 and 2 mm, over the surface of the protector which faces the inflation air, preferably assuring continuity by contact with the layer 6. An extension of the layer 8 on the outer side (between the bead and the hook of the rim) is excluded in order to preserve a good clamping of the tire on the rim. In another version, the layer of rubber 8 covers substantially a part of the protector which is in contact with the rim with or without a slight covering of the inner surface of the protector 7 which is directed towards the inflation air. In another version, the layer of rubber 8 covers substantially the part of the protector which faces the inflation air, with a slight radially inner covering in an axially outward direction of a part of the protector 7 in contact with the rim.

Various practical embodiments of the invention are possible: for example, the different layers of rubber of the zone of the beads can be placed one by one on the tirebuilding drum in conventional manner, first the impermeable rubber layer 8, then the layer-6 which is to come in contact or superposition with it, then the layer 7, and then the other components, added in customary manner. In the event that the rubbers 8 and 6 are of the same composition, it is 8 also possible to deposit them in a single step and then put the protector 7 in position. Another embodiment consists in preparing in advance the layer of protector 7 provided with a layer of impermeable mix 8 and, in a single operation, placing this assembly on the tire-building drum before or after the layer 6, or on the blank of the raw tire. The assembly 7 plus 8 can be produced by stacking layers obtained by calendering or by coextrusion. The layer 8 can also be applied on the cured tire. The layer 8 can also be obtained by applying a fluid dispersion of the components of the mix, also on the raw tire or else after curing. The layer 8 can be applied upon retreading operations or even upon inspection dismountings and maintenance operations of the tires, which makes it possible to treat tires which have still not benefitted from this improvement and to repair beads of tires in accordance with the invention. The vulcanization of layer 8 applied on a cured tire may be effected by heating for rubbers which do not vulcanize at ambient temperature.

A truck tire provided with beads in accordance with the invention which has been subjected to a prolonged travel test exhibits a substantially intact protector 7 which still assures\ good tightness, while the protector 7 of a control tire in accordance with the prior art is greatly hardened by thermal oxidation and may even exhibit cracks. Furthermore, the commencements of separation of the cables of the carcass reinforcement 1 in the zone of the beads are far less 9 numerous in the event that the protector is covered with the layer of rubber 8. It is generally noted that the beads in accordance with the invention make it possible to triple the duration of the travel tests before obtaining the same level of degradation as those of the prior art.

Claims

1. A tubeless tire which has a carcass reinforcement integral with bead rings in beads and is covered on the inside with a layer of rubber of slight modulus of extension at 10% elongation which is impermeable to air used for inflation of the tire, the beads being covered, at least in the part thereof in contact with a mounting rim, by circumferential profiled members known as protectors, formed of non-impermeable rubbers of great modulus of extension at elongation, characterized by the fact that the protectors are partially covered, at least radially to the inside and axially towards inside, by a layer of impermeable rubber mix formed from a cross linkage elastomeric material of a coefficient of permeability for air at 80 0 C of less than 21x10 1 7 x m 2 sxPa and of a thickness I of between 0.1 and 1 mm, covering the radially inner part of the protector over of an axial length LO, such that the ratio LO/L1 to the axial width L1 of the bead is between 0.2 and 0.7.

2. A tire according to claim 1, characterized by the fact that the layer of impermeable mix is extended towards the inside in a radial direction over the surface of the protector which faces the inflation air by a layer of impermeable mix of a thickness of between 0.1 and 2 mm, assuring continuity with the inner rubber

3. A tire according to any one of claims 1 to 2, characterized by the fact that the layer of impermeable mix has a coefficient of permeability for air at of less than 14x 10-"xm 2 s xPa 11

4. A tire according to any one of claims 1 to 2, characterized by the fact that the layer of impermeable mix has a coefficien, of permeability for air at of less than 7 x 10 17 2 m sxPa A tire according to any one of claims 1 to 4, characterized by the fact that the layer of impermeable mix has a modulus at 10% elongation E10 force/ initial section of between 1.5 and 8 MPa.

6. A method of producing the tire as defined in any one of claims 1 to characterized by the fact that the protective profiled member provided with its layer of impermeable rubber mix is placed on a building drum or a blank of a tire in an uncured condition in a single operation.

7. A method of producing the tire as defined in any one of claims 1 to characterized by the fact that the layer of impermeable rubber mix is placed on a the tire in an uncured or cured condition. *o

8. A method of producing the tire as defined in any one of claims 1 to characterized by the fact that the layer of impermeable rubber mix is obtained by application of a fluid dispersion of each component of the mix onto o the tire in an uncured or cured condition. DATED this 6th day of February, 1997 COMPAGNIE GENERAL DES ETABLISSEMENTS MICHELIN MICHELIN CIE WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA AU3257593.WPC[DOC. 007] SKP/KWB:JL[EK] Case 769 Title: Beads of tubeless tires and methods for producing them. Applicant: Compagnie Generale des Etablissements Michelin Michelin Cie. Abstract The invention concerns the structures and production of tubeless tire beads the seal of which on the rims and the resistance to degradations of which are increased. The beads, at least the surfaces of which in contact with the rims are formed of protective mixes are covered, in accordance with the invention, with an impermeable mix at least in part over the portion of the protector in contact with the rim. Extension of the covering over the surface of the protector which is in contact with the inflation air is desirable.